As described in Patent Literature 1 (JP 2004-077887 A), a conventional technology is known in which a soft photocurable resin is filled between a touch panel and a display element when a display panel provided with the touch panel is assembled. The photocurable resin functions as a buffer material for protecting the display panel from stress. In addition, in displays for televisions or personal computers, a photocurable resin is also used to be filled between a display element and a protection layer made of an acrylic plate or a glass plate. However, since a refractive index of an adherend is changed depending on a material of the adherend, a refractive index of the photocurable resin needs to be changed so as to match the refractive index of the adherend, from the viewpoint of optical properties. The refractive index of the photocurable resin is determined according to a raw material and composition of the photocurable composition before curing. Therefore, in the photocurable composition, it is difficult to balance physical properties such as heat resistance and moisture resistance with optical properties while adjusting optical properties. In particular, there is known a case where, when the photocurable resin absorbs moisture, the photocurable resin becomes cloudy and thus optical properties are decreased or a case where the photocurable resin becomes yellow due to heat. On the other hand, in order to improve heat resistance (in an atmosphere at 60° C. for 1,000 hours) or moisture resistance (in an atmosphere at 85° C.×85 RH % for 1,000 hours), it is preferable to increase a glass transition temperature. However, at this time, there is a concern in yellow discoloration of the cured product. Moreover, it is assumed that the cured product does not function as a buffer material because the cured product becomes harder such. Therefore, there is a problem in the balance between optical properties and physical properties.
In addition, when an oligomer having a long main skeleton and a small number of (meth)acrylic groups included per one molecule is used in a soft photocurable resin, a cured product becomes softer. However, photocurability is decreased due to the structure. According to this, a non-cured portion may remain depending on ways of irradiation with light and a film thickness of the cured product may also be very thin. As described in Patent Literature 2 (JP 2009-186955 A, WO 2008/123611 A), a shadow zone is not cured unless a method of irradiation with light from the side surface of a display element is employed. Moreover, even in the case of irradiation with light from a touch panel side, the light irradiation is partially absorbed at a touch panel member and thus an integrated light amount of light reaching to the photocurable resin is decreased. Therefore, there is a concern in that, when thick film curability is low, a cured state is unstable. Moreover, in the case of a display panel in which a touch panel is used as an outermost layer or a protection layer is used instead of the touch panel, if a refractive index of the outermost layer and a refractive index of the photocurable resin do not match with each other, optical properties cannot be achieved. Therefore, when one kind of the photocurable resin is used, it is not possible to achieve sufficient optical properties with respect to any types of the outermost layer.